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Date: Wed, 7 Sep 2011 17:52:57 +0200
From: Lukas Czerner <lczerner@...hat.com>
To: linux-ext4@...r.kernel.org
Cc: tm@....ma, tytso@....edu, Lukas Czerner <lczerner@...hat.com>
Subject: [PATCH v3] ext4: fix possible overflow in ext4_trim_fs()
The overflow can happen when we are calling get_group_no_and_offset()
which stores the result of do_div() in 32 bit long type. However the
result might be bigger than that if big blocknr is passed in. This will
most likely happen when calling FITRIM with the default argument len =
ULLONG_MAX.
Fix this by using "end" variable instead of "start+len" as it is easier
to get right and specifically check that the end is not beyond the end
of the file system, so we are sure that the result of
get_group_no_and_offset() will not overflow. Otherwise truncate it to
the size of the file system.
Signed-off-by: Lukas Czerner <lczerner@...hat.com>
---
v2 - Change commit description to better describe the problem
v3 - Use end instead of start+len, rework the fix
fs/ext4/mballoc.c | 43 +++++++++++++++++++++++--------------------
1 files changed, 23 insertions(+), 20 deletions(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 17a5a57..fa8b14b 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4946,37 +4946,36 @@ out:
int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
{
struct ext4_group_info *grp;
- ext4_group_t first_group, last_group;
- ext4_group_t group, ngroups = ext4_get_groups_count(sb);
+ ext4_group_t group, first_group, last_group;
ext4_grpblk_t cnt = 0, first_block, last_block;
- uint64_t start, len, minlen, trimmed = 0;
+ uint64_t start, end, minlen, trimmed = 0;
ext4_fsblk_t first_data_blk =
le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
+ ext4_fsblk_t max_blks = ext4_blocks_count(EXT4_SB(sb)->s_es);
int ret = 0;
start = range->start >> sb->s_blocksize_bits;
- len = range->len >> sb->s_blocksize_bits;
+ end = start + (range->len >> sb->s_blocksize_bits) - 1;
minlen = range->minlen >> sb->s_blocksize_bits;
- if (unlikely(minlen > EXT4_BLOCKS_PER_GROUP(sb)))
+ if (unlikely(minlen > EXT4_BLOCKS_PER_GROUP(sb)) ||
+ unlikely(start > max_blks))
return -EINVAL;
- if (start + len <= first_data_blk)
+ if (unlikely(end >= max_blks))
+ end = max_blks - 1;
+ if (end <= first_data_blk)
goto out;
- if (start < first_data_blk) {
- len -= first_data_blk - start;
+ if (start < first_data_blk)
start = first_data_blk;
- }
/* Determine first and last group to examine based on start and len */
ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) start,
&first_group, &first_block);
- ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) (start + len),
+ ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) end,
&last_group, &last_block);
- last_group = (last_group > ngroups - 1) ? ngroups - 1 : last_group;
- last_block = EXT4_BLOCKS_PER_GROUP(sb);
- if (first_group > last_group)
- return -EINVAL;
+ /* The last block to discard in the group */
+ end = EXT4_BLOCKS_PER_GROUP(sb);
for (group = first_group; group <= last_group; group++) {
grp = ext4_get_group_info(sb, group);
@@ -4990,22 +4989,26 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
/*
* For all the groups except the last one, last block will
* always be EXT4_BLOCKS_PER_GROUP(sb), so we only need to
- * change it for the last group in which case start +
- * len < EXT4_BLOCKS_PER_GROUP(sb).
+ * change it for the last group, note that last_block is
+ * already computed earlier by ext4_get_group_no_and_offset()
*/
- if (first_block + len < EXT4_BLOCKS_PER_GROUP(sb))
- last_block = first_block + len;
- len -= last_block - first_block;
+ if (group == last_group)
+ end = last_block;
if (grp->bb_free >= minlen) {
cnt = ext4_trim_all_free(sb, group, first_block,
- last_block, minlen);
+ end, minlen);
if (cnt < 0) {
ret = cnt;
break;
}
}
trimmed += cnt;
+
+ /*
+ * For every group except the first one, we are sure
+ * that the first block to discard will be block #0.
+ */
first_block = 0;
}
range->len = trimmed * sb->s_blocksize;
--
1.7.4.4
--
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